Recently, it has become popular to process and manage the sound and video in digital format in appliances such as acoustic appliances and video appliances. Such trends in digital encoding of sound and video in appliances such as acoustic appliances are extending to the field of radio broadcasting. For example, in the United States, a digital radio broadcasting system called IBOC (In Band On Channel) is proposed and made available by iBiquity Digital Corp.
Meanwhile, conventional analog radio broadcasting broadcasts via carrier wave (hereinafter referred to as “analog carrier wave”) that has frequency distribution inside the frequency band (hereinafter referred to as “channel” or “frequency channel”) assigned to individual broadcasting stations. Actually, in order to avoid the interference between analog carrier wave of adjacent channels, only the center portion of the assigned band is used for the transmission of the analog carrier wave, and other portions are not used. It is noted that “digital radio broadcasting” in this application means “IBOC digital radio broadcasting”.
IBOC is a type of digital radio broadcasting that uses frequency channel assigned to the conventional analog radio broadcasting. In IBOC standard, a plurality of signal formats are defined, such as hybrid format in which the digital radio broadcasting signal is multiplexed onto the conventional analog radio broadcasting signal, and all-digital format consisted of only digital signals, and it is designed to gradually transfer from conventional analog radio broadcasting to all-digital radio broadcasting that has many functions and is high in quality. In the IBOC, digital broadcasting signals are transmitted with Orthogonal Frequency Division Multiplexing (OFDM) that uses many carrier waves (subcarriers).
In the IBOC standard, signal format called “hybrid format” is used in the transition period from analog broadcasting to all-digital broadcasting. In the hybrid format, the digital radio broadcasting, which allocates the subcarrier of digital broadcasting in the portion that is adjacent to the center portion of the frequency channel that the analog carrier wave uses and that was not conventionally used (Hereinafter referred to as “sideband”) is broadcast using the modulated wave of the sideband of the band. In other words, in accordance with the hybrid format of the IBOC, the band for frequency channel assigned for the conventional analog radio broadcasting is utilized effectively, and the analog radio broadcasting and the digital radio broadcasting are simultaneously transmitted using a same channel. It is noted that, depending on the frequency channel, a plurality of subchannels (programs) may be transmitted using a plurality of logic channels for the digital radio broadcasting. In the following, the channel that includes a plurality of subchannels in a single frequency channel is referred to as “multichannel”. Further, “digital, radio broadcasting” means “IBOC digital radio broadcasting” in this application.
For example, Japanese Patent Provisional Publication No. JP2005-12593 A1 (hereinafter referred to as “the Reference Document”) discloses an IBOC broadcasting receiver that is capable of receiving such IBOC digital radio broadcasting. The IBOC broadcasting receiver disclosed in the Reference Document is provided with automatic seeking function for seeking a receivable channel.
The IBOC broadcasting receiver starts the channel seeking operation when a predetermined user operation (e.g., pressing down once the “tuning-up” or “tuning-down” button equipped at the operation Panel) is performed, and the receiving intensity of the seeking frequency channel is detected. Then, based on the detected result, it determines whether frequency channel is station-existent (i.e., a state where a broadcasting station is found) or not, and if it determined that it is station-existent, it determines whether the digital radio broadcasting is transmitted in the frequency channel or not. Then, if it determined that the digital radio broadcasting is being transmitted, the seeking operation is stopped with the frequency channel being selected, and the digital radio broadcasting of the selected frequency channel is played. Further, if it determined that the digital radio broadcasting is not being transmitted, similar process is performed on the next seeking frequency channel. This process is repeatedly performed until digital radio broadcasting is performed the seek.